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[ricknroll]

I have a friend who purchased a CD lathe after he heard a comparison between a regular CD and a second copy of the CD treated with the CD lathe.  The theory is that by smoothing out the rough edges of the CD with the lathe, the disc can spin more evenly, thereby reducing mechanical jitter.  Even though this sounded bogus to me, I tried to keep an open mind and suggested the following test: I brought over some CDs my friend and I have in common and we compared my uncut CDs to his treated ones.  Although it was not a double-blind test (I was operating the CD player with full knowledge of which CD I was playing), my friend was unable to distinguish between his treated CDs and my regular ones.  He admitted as much, although he attributed this to his acoustically lousy room, claiming that in the stereo store he purchased the lathe from, the room was much better sounding and the difference between regular and treated CDs was night and day.  I am skeptical of this claim, but to his credit, he did return the CD lathe to the store for a full refund.

My question is:  Is there any merit to claims of audible mechanical jitter caused by CDs/CD players or other digital devices?  In this example, when I say mechanical jitter, I mean jitter induced by mechanical vibrations in the transport mechanism, not jitter caused by a lousy clock during the DA conversion.  It seems at least possible to me that hard drives would be less prone to this type of error, since CDs are removable media and presumably the transport mechanism in a CD player is not as precise as a hard drive assembly.  On the other hand, I don't know if mechanical jitter is ever audible, or if CDs really suffer from this problem.

Thanks,

Rick

[danlavry]

ricknroll wrote on Tue, 26 July 2005 21:59

I have a friend who purchased a CD lathe after he heard a comparison between a regular CD and a second copy of the CD treated with the CD lathe.  The theory is that by smoothing out the rough edges of the CD with the lathe, the disc can spin more evenly, thereby reducing mechanical jitter.  Even though this sounded bogus to me, I tried to keep an open mind and suggested the following test: I brought over some CDs my friend and I have in common and we compared my uncut CDs to his treated ones.  Although it was not a double-blind test (I was operating the CD player with full knowledge of which CD I was playing), my friend was unable to distinguish between his treated CDs and my regular ones.  He admitted as much, although he attributed this to his acoustically lousy room, claiming that in the stereo store he purchased the lathe from, the room was much better sounding and the difference between regular and treated CDs was night and day.  I am skeptical of this claim, but to his credit, he did return the CD lathe to the store for a full refund. My question is:  Is there any merit to claims of audible mechanical jitter caused by CDs/CD players or other digital devices?  In this example, when I say mechanical jitter, I mean jitter induced by mechanical vibrations in the transport mechanism, not jitter caused by a lousy clock during the DA conversion.  It seems at least possible to me that hard drives would be less prone to this type of error, since CDs are removable media and presumably the transport mechanism in a CD player is not as precise as a hard drive assembly.  On the other hand, I don't know if mechanical jitter is ever audible, or if CDs really suffer from this problem. Thanks, Rick

I never heard of such a thing, though I understand that one can have well made CD's, and also terrible CD manufacturing.

But I do know that one needs to make sure that any comparison is done very properly.

There are a lot of ways to have "A" sound better then the "B", even if they are "the same". The most known way to do so is to play "A" louder then "B". It does not take much extra loudness to convince that "the same thing" sounds better. A .1dB level matching or better is a must. It is the "first rule" when setting up listning tests.

Unfortunately, a few audio sales guys do take advantage of slight level mismatch and other such "concepts". That may account for some of the discrepancies such as you described.

Of course many audio dealers make sure that the comparisons are done the right way.

Regards
Dan Lavry
www.lavryengineering.com  

[ricknroll]

Just for kicks, here's a review of one such CD lathe:   http://www.enjoythemusic.com/magazine/equipment/0603/audiode sk.htm

My personal belief/suspicion is that treating CDs with such a product will not affect the sound, but I'm curious if there is any merit to the theory of how this is supposed to help or if the type of jitter this thing is supposed to fix is a nonexistent problem in the first place.

-Rick

[danlavry]

ricknroll wrote on Tue, 26 July 2005 23:45

Just for kicks, here's a review of one such CD lathe:    http://www.enjoythemusic.com/magazine/equipment/0603/audiode sk.htm My personal belief/suspicion is that treating CDs with such a product will not affect the sound, but I'm curious if there is any merit to the theory of how this is supposed to help or if the type of jitter this thing is supposed to fix is a nonexistent problem in the first place. -Rick

I wasted some time trying to read the explanation regrading what makes it work. I did not even find an attempted explanation.

I once saw an ad for a CD de-magnetizer! (CD's are optical, non magnetic devices)....

Regards
Dan Lavry
www.lavryengineering

[trevord]

There are so many mechanical problems with a cd player, the "jitter" or "wobble" caused by imperfections in the cd is the least of them.
This is why data from the cd is buffered, up to 10 seconds in some cases. This is mainly to deal with the bumps in portable players.
But you can be assured.. you cannot hear any mechanical artifact from reading the cd.

The only caveat to this is if the cd disk or player is vibrating so badly that it is causing errors and the player cannot handle the number of errors in the buffer time, then you may hear pops and clicks, but if you have errors which cannot be handled in the huge amount of time provided by the buffer you may hear a "drop out" not bad quality audio..

Of course after the buffer, you have the problems associated with d to a conversion and the effect of the quality of the d to a components.

[Sahib]

Unfortunately CD lathe is one of those bs like timber potentiometer knobs that enhances the sound clarity of an amplifier. I also heard of upgrading a CD player by spraying the inner black plastic surface of the transport mechanism in green. Apparently it helped eliminate the reflections of the stray beam that came out of the reading head.  How unfortunate that people are getting really robbed. Alternatively, how stupid the people are. But then again there is a saying, if everybody was clever, how a conmen would make a living? Or something like that.

[maxdimario]

There is good and bad in everything.

97% of Hi-fi culture is bullshit, In my personal opinion.

The remaining 3% is worth following, and can provide some very useful insights. In my personal opinion.

There is no data to back up the aforementioned statements.

But, yeah... once a buffer comes into the equation, small mechanical vibrations like that will not affect the output because of error correction etc.

[Ronny]

Although the cd gizmo is pure hogwash, there are elements of mechanical vibration (I wouldn't call it jitter as to not confuse with converter or line jitter) that are measured and kept under guidelines. For example speed ratings on cd-r blanks are relative to mechanical vibration, the difference between a 12x and a 52x disk is that the 52x disk can be written up to 52 times real time speed before vibration becomes a factor. A basic explanation is that the 52x disks are more balanced, sort of like the difference between a balanced tire and an unbalanced tire. When the tires are running slow, the unbalanced tire and the balanced tire feel the same, but when you reach a certain speed on the unbalanced tire, oscillation exceeds recovery and the wheel hops trying to catch up, losing some traction. When that happens while burning a cd, the pre-groove wobble which is normal goes to far outside of the pre-groove resulting in unrecoverable errors at best and a coaster kicked out at the worst.

[Loco]

Ronny wrote on Wed, 27 July 2005 22:04

the difference between a 12x and a 52x disk is that the 52x disk can be written up to 52 times real time speed before vibration becomes a factor. A basic explanation is that the 52x disks are more balanced

Hell no! I'm absolutely sure that's not the case. The speed is related to the reflectivity of the surface as well as it's reaction speed to the laser at the time of burning.

[Ronny]

Loco wrote on Thu, 28 July 2005 11:50

Ronny wrote on Wed, 27 July 2005 22:04 the difference between a 12x and a 52x disk is that the 52x disk can be written up to 52 times real time speed before vibration becomes a factor. A basic explanation is that the 52x disks are more balanced Hell no! I'm absolutely sure that's not the case. The speed is related to the reflectivity of the surface as well as it's reaction speed to the laser at the time of burning.

Before you confirm yourself to being absolutely sure, let me remind you that no matter what speed a disk is recorded at, they will all play back at 1x and reflectivity is not an issue on the burn, only on the playback. Understand? Also, the higher speed disks have a thinner dye layer so that the data can be burned faster and it doesn't matter what speed the disk is "rated" for, it can only be burned at the max speed that the burner supports, for example I have 52x Plextors and 12x Plextors, stick a 52x Taiyo in the 12x and it will only burn tops of 12 times. In fact the 52x burners seldom burn at more than 48x. Recording speeds are never fixed, if you set it to 4x, than it's going to operate between 3 and 5x and 4x will be the average.


5. What does the "X" stand for?
The "X" of discs is a measure of how fast they can be recorded in a drive rated to be capable of that speed. A 32X disc can be recorded at 32 times normal speed (normal is the playback speed of a music CD). A 32X disc will record in a drive rated at 32X, but only at 16X speed in a drive rated only for 16X maximum.
(Back To Top)

6. Why won't my 48X recorder record at 48X?
There could be several reasons for this.
1) The CD-R disc may not be 48x compatible so the drive will bump down its recording speed.
2) System performance may be poor causing slow data transfer and thus unreliable recording at 48x.
3) Authoring software may need to be updated.
(Back To Top)

7. Are 52X discs better than 16X discs?
Faster discs have thinner dyes that react faster to the laser light and the greater laser power used. There is no quality difference in this regard, although discs rated at the highest speeds have to have excellent balance, concentricity, and uniformity so that they do not cause problems for high speed drives.


Reprinted from Nashua cd manufacturers guideline.

[Loco]

Ronny wrote on Thu, 28 July 2005 16:42

Loco wrote on Thu, 28 July 2005 11:50 Ronny wrote on Wed, 27 July 2005 22:04 the difference between a 12x and a 52x disk is that the 52x disk can be written up to 52 times real time speed before vibration becomes a factor. A basic explanation is that the 52x disks are more balanced Hell no! I'm absolutely sure that's not the case. The speed is related to the reflectivity of the surface as well as it's reaction speed to the laser at the time of burning. Before you confirm yourself to being absolutely sure, let me remind you that no matter what speed a disk is recorded at, they will all play back at 1x and reflectivity is not an issue on the burn, only on the playback. Understand? Also, the higher speed disks have a thinner dye layer so that the data can be burned faster and it doesn't matter what speed the disk is "rated" for, it can only be burned at the max speed that the burner supports

You got it all wrong. Read carefully what you wrote and you will see that you can burn any CD at any speed under the rated speed, not just the maximum speed.

Quote:

Faster discs have thinner dyes that react faster to the laser light and the greater laser power used. There is no quality difference in this regard, although discs rated at the highest speeds have to have excellent balance, concentricity, and uniformity so that they do not cause problems for high speed drives.

The discs are faster because of the dyes, not because they are better balanced. An old Taiyo 16X most likely will be better balanced than a new 48X Memorex.

[Ronny]

Loco wrote on Thu, 28 July 2005 18:09

Ronny wrote on Thu, 28 July 2005 16:42 Loco wrote on Thu, 28 July 2005 11:50 Ronny wrote on Wed, 27 July 2005 22:04 the difference between a 12x and a 52x disk is that the 52x disk can be written up to 52 times real time speed before vibration becomes a factor. A basic explanation is that the 52x disks are more balanced Hell no! I'm absolutely sure that's not the case. The speed is related to the reflectivity of the surface as well as it's reaction speed to the laser at the time of burning. Before you confirm yourself to being absolutely sure, let me remind you that no matter what speed a disk is recorded at, they will all play back at 1x and reflectivity is not an issue on the burn, only on the playback. Understand? Also, the higher speed disks have a thinner dye layer so that the data can be burned faster and it doesn't matter what speed the disk is "rated" for, it can only be burned at the max speed that the burner supports You got it all wrong. Read carefully what you wrote and you will see that you can burn any CD at any speed under the rated speed, not just the maximum speed. Quote: Faster discs have thinner dyes that react faster to the laser light and the greater laser power used. There is no quality difference in this regard, although discs rated at the highest speeds have to have excellent balance, concentricity, and uniformity so that they do not cause problems for high speed drives. The discs are faster because of the dyes, not because they are better balanced. An old Taiyo 16X most likely will be better balanced than a new 48X Memorex.

No you need to go back and reread what I wrote as you clearly don't understand. I never said that you had to burn a cd at it's max speed rating. I said quite the opposite that the speed is limited by the burner capability, so it doesn't matter if you stick a 52x blank into a 12x burner, it's not going to burn above 12x.

What is it about this that you don't understand:

There is no quality difference in this regard, although discs rated at the highest speeds have to have excellent balance, concentricity, and uniformity so that they do not cause problems for high speed drives.

The dye is thinner and the blanks have to be better balanced, just like my tire anology. Vibration as I said in the beginning is the main factor, because it doesn't matter how thin the dye is, if the disk is not balanced the laser focus on the dye will be skewed.  

[Loco]

Ronny wrote on Thu, 28 July 2005 22:29

No you need to go back and reread what I wrote as you clearly don't understand. I never said that you had to burn a cd at it's max speed rating.

Well, you said "it doesn't matter what speed the disk is rated for, it can only be burned at the max speed that the burner supports". A syntax mishap?

Quote:

The dye is thinner and the blanks have to be better balanced, just like my tire anology. Vibration as I said in the beginning is the main factor, because it doesn't matter how thin the dye is, if the disk is not balanced the laser focus on the dye will be skewed.

Vibration is NOT the main factor. you can balance any tire for 200 mph, but the thread ans sidewalls must be designed and rated ZR in order to be useable. Properly balanced, you can spin a CD at 1000X if you want to, but you can't burn it at that speed unless the dye is designed for it.

Sheezzz.....

[Ronny]

Loco wrote on Fri, 29 July 2005 10:00

Ronny wrote on Thu, 28 July 2005 22:29 No you need to go back and reread what I wrote as you clearly don't understand. I never said that you had to burn a cd at it's max speed rating. Well, you said "it doesn't matter what speed the disk is rated for, it can only be burned at the max speed that the burner supports". A syntax mishap? Quote: The dye is thinner and the blanks have to be better balanced, just like my tire anology. Vibration as I said in the beginning is the main factor, because it doesn't matter how thin the dye is, if the disk is not balanced the laser focus on the dye will be skewed.   Vibration is NOT the main factor. you can balance any tire for 200 mph, but the thread ans sidewalls must be designed and rated ZR in order to be useable. Properly balanced, you can spin a CD at 1000X if you want to, but you can't burn it at that speed unless the dye is designed for it. Sheezzz.....

Ok, you're right.

[Ronny]

I just ran across someone that uses the same tire analogy that I use. They also give redbook specs on balance tolerances allowed and explain why it is the main factor in high speed disks becoming unreliable and also detrimental to the bearings on the drive.

Media Sciences:


http://www.mscience.com/faq17.html